Motorized boat lifts provide the benefit of increased lift over a manually-driven lift. Small AC motors are generally cheaper than their DC counterparts, but provide inferior speed and torque control.
For example, U.S. Pat. No. 7,377,485 to Davis discloses a three-phase drive motor is utilized to operate a boat lift.
Many drive systems used in boat lifts use threaded shafts for driving a worm gear, a straight shaft using a nut and bolt coupling, or sprocket and roller chain mechanisms. U.S. Pat. No. 7,059,803 to Floe, discloses a boatlift leg and frame structure utilizing a ball screw lifting mechanism.
U.S. Pat. No. 6,033,148 to Norfolk comprises “a drive shaft carrying a drive pulley, a pulley belt entrained about the drive pulley and a driven pulley, the driven pulley being connected to a shaft of a worm gear, the worm gear being in mesh with a drive gear, and the drive gear being connected to an output shaft which is in turn connected to a reel having wound thereon a boat lift cable which is connected to a boat platform for lifting and lowering a boat resting thereon.” However, a disadvantage of a worm gear is that the worm (screw) drives the gear; the gear does not drive the worm. This provides a self locking mechanism which is appropriate to certain applications, for example the winding component of a stringed instrument, where you want to hold a position. However, this can be a disadvantage when routinely raising and lowering boats on a lift.
In another example, U.S. Pat. No. 7,383,781 to Griffin discloses a boat lift system for raising and lowering a boat from and into a body of water includes a cradle, a cable and a drive system. The cradle is configured to hold the boat. Griffin discloses a drive sprocket system.
In another example, U.S. Pat. No. 4,832,210 to Wood discloses a boat lift assembly wherein the use of a conventional cable system has been replaced with a screw drive assembly.
Other prior art boatlift structures have also disclosed the use of an electronic controller, as disclosed in U.S. Pat. No. 7,059,803 to Floe. However, these and other problems disclosed in the prior art have not been adequately addressed by the prior patents.